1. Field of the Invention
The present invention relates to methods and compositions used to protect growing plants from fungal diseases.
2. Technical Background
As a result of increasing concern over environmental safety of non-degradable synthetic products and food safety, there is a demand for natural degradable products as alternatives for protecting agricultural products both during and after growth season from a variety of environmental pathogens.
The protection of desirable plants and their produce from fungal pathogen infection has traditionally required preventative applications of fungicidal agents. Fungicidal compounds have long been used to increase yields and extend agricultural production capabilities into new areas. They have also been extremely important tools for ameliorating season-to-season differences in yield and quality caused by weather-driven variations in disease pressure.
The future role of fungicides in agriculture is increasingly threatened by several factors including the development of pest resistance, increasing concerns about food safety, and environmental accumulation of toxic compounds. As older fungicides are removed from the market due to regulatory changes, and new fungicides are becoming increasingly expensive to register, there is an increasing need to find ways to more wisely use the remaining, safest fungicides. This is particularly true for the many crop/disease combinations which do not represent large enough markets to pay for the cost of new compound registration. Wiser fungicide use will include ways to reduce application rates (and thus potential residues), finding ways to extend registrations to new crops, and identifying new fungicidal compositions and treatments to combat the development of pest resistance.
Chemical fungicides have provided an effective method of control; however, the public has become concerned about the amount of residual chemicals which might be found in food, ground water and the environment. Stringent new restrictions on the use of chemicals and the elimination of some effective pesticides from the market place could limit economical and effective options for controlling fungal growth.
The commercialization of disease biocontrol agents has been hampered by inconsistent field performance. Organisms which show biocontrol potential in laboratory and greenhouse experiments often fail to compete with the existing microflora when applied outdoors and are thus unable to express their biocontrol potential, regardless of mode of action. Specifically there is a need for disease control methods which are more compatible with the need for affordable and effective disease control, a high degree of food safety, and minimal environmental impact.
One example of fungal infection during the growth season of grapes is powdery mildew caused by Uncinula necator. Infection can result in severe damage even in dry areas such as California. Traditionally this disease was controlled with applications of elemental sulfur, but this necessitates frequent, high volume applications of an irritating material. The introduction of egosterol biosynthesis inhibiting fungicides (primarily triazoles) greatly simplifies control, but also selects for tolerant strains. Some of these compounds are also known to have potential teratogenic effects and very long soil residuals. In these and other examples, alternative control methods are in great demand—particularly methods which are safer or more environmentally benign.
A new class of peptide-polysaccharides has been recently introduced. McArdle in U.S. Pat. Nos. 5,942,123, 5,747,416, 5,645,880, discloses these peptide-polysaccharides for a number of uses. However, there has been no suggestion or recognition of their use as inhibiting fungal growth on plants during the growth season.